There appears to be some disagreement, though we can assume it's an extremely friendly disagreement, over who invented the concept of the "random act of kindness". Credit usually goes to the American peace activist Anne Herbert, who reportedly coined it - and its counterpart, the "senseless act of beauty" - on a napkin in the early 80s. Then again, a Californian college professor, Chuck Wall, claims to have thought it up in 1993; today, he tours as a motivational speaker and sells keyrings and fridge magnets extolling the virtues of spontaneous generosity. (Why not try asking him to send you some for free?) Every few years, the notion gets rediscovered as if it were new - by Oprah, in the movie Pay It Forward, or in Danny Wallace's book Yes Man; there are at least five other books on the topic. All of which baffles me slightly, since the only time I've been on the receiving end of an RAK - I was buying a sandwich in an airport when the woman ahead of me paid for it, vanishing before I could thank her - I wasn't suffused with a warm sense of humanity's interconnectedness. I was suffused with a feeling best expressed by an acronym that's popular online: WTF?

Maybe I'm atypically misanthropic. Or maybe not: the handful of studies conducted into people's responses to random generosity at least partly back me up. We know bestowing kindness boosts the giver's mood. But recipients - according to a 2000 study in which researchers handed gifts to members of the public - are frequently hostile. "If someone randomly does something kind for me, I'm on guard. I don't think that shows a fundamental cynicism or a deep distrust of mankind," writes Gretchen Rubin, on the excellent blog The Happiness Project. "It just shows that I think that most people act purposefully, and if I don't understand the purpose, I question their motives. It's not the kindness of the act that's the problem; it's the randomness." This isn't to denigrate every good turn advocated by proponents of RAK. But the good ones aren't really random. Helping someone who's struggling with their shopping, say, is a targeted act. Random behaviour disorients us.

Specifically, we wonder what the giver wants in return: reciprocity is so fundamental to human relationships, we assume something must be expected of us, too. Crafty salespeople can exploit this expectation: as the psychologist Robert Cialdini notes in his book Influence, we're so deeply primed to reciprocate generosity that customers who receive a free gift become far more likely to make a purchase "in return". (It works even when they dislike the seller. The reciprocity rule, Cialdini writes, "possesses awesome strength, often producing a 'yes' response to a request that, except for an existing feeling of indebtedness, would surely have been refused.") There's a reason the Hare Krishnas hand out flowers before soliciting donations: adopting that fundraising tactic transformed their finances.

Some despair of people like me, who are freaked out by the kindness of strangers: has trust in others really been so depleted? But there's something uncomfortably self-absorbed about an RAK that thrills the giver while confusing the receiver, or triggering their inbuilt propensity to feel indebted. Here's to non-random, thought-through, rationally targeted kindness: a rubbish bumper-sticker slogan, lacking in anarchist pizazz, but surely, on balance, a rather better thing.